Exercise and cardiovascular risk among breast cancer patients.

12022 Background: Breast cancer is the most common cancer among U.S. females, accounting for 15% of new diagnoses. As survivorship increases, cardiovascular disease (CVD) has become a major cause of long-term morbidity and mortality. Survivors remain at elevated risk for CVD due to treatment-related cardiotoxicity and underlying risk factors. Despite this growing burden, evidence on whether exercise mitigates cardiac dysfunction remains limited and inconsistent. This study examines the association between physical activity and subsequent CVD and mortality outcomes among breast cancer patients with documented Exercise Vital Sign (EVS) data. Methods: A retrospective cohort study was conducted within the Kaiser Permanente Southern California (KPSC) health system. Adult members (≥18 years) with primary breast cancer diagnosed from 2011–2019 were identified through the KPSC cancer registry. Eligible patients had ≥12 months of continuous enrollment and at least two encounters (separated by ≥1 month) with EVS data in the year prior to diagnosis. Physical activity was defined using median exercise volume: completely inactive (0 min/week; reference), insufficiently active (IA; > 0– < 149 min/week), and sufficiently active (SA; ≥150 min/week). Outcomes included all-cause, cancer-specific, and CVD mortality; congestive heart failure (CHF); cardiomyopathy; and major adverse cardiovascular events (MACE). Cox proportional hazards models adjusted for demographic factors, lifestyle characteristics, tumor features, insurance type, and pre-existing cardiovascular comorbidities. Results: Among the cohort (N = 12,481), compared with the completely inactive group, SA was associated with lower risk of CHF (HR 0.74; 95% CI 0.59–0.89). For MACE, both IA (HR 0.78; 95% CI 0.71–0.86) and SA (HR 0.66; 95% CI 0.59–0.74) demonstrated decreased risk. Similar reductions were observed for all-cause mortality (IA HR 0.75; 95% CI 0.68–0.83; SA HR 0.62; 95% CI 0.54–0.70), cancer-specific mortality (IA HR 0.82; 95% CI 0.71–0.96; SA HR 0.69; 95% CI 0.57–0.83), and CVD mortality (IA HR 0.68; 95% CI 0.58–0.79; SA HR 0.53; 95% CI 0.43–0.65). Physical activity was not associated with reduced cardiomyopathy risk. Conclusions: Physical activity appears to reduce cardiovascular and mortality risk among breast cancer survivors in a dose-responsive manner, with SA patients experiencing the greatest benefit. Even insufficient activity was associated with improved prognosis compared with complete inactivity, supporting the incorporation of exercise promotion into survivorship care. Regular physical activity may reduce CVD and mortality risk among breast cancer survivors, supporting routine EVS screening and referral to exercise or cardio-oncology programs in survivorship care. These findings also reinforce the need for institutional and payer policies that prioritize exercise assessment and counseling as standard components of cancer survivorship care.